The present invention relates to a plate-mounting member which is used to mount a plate onto a plate cylinder disposed in a printing apparatus or a plate-making apparatus. The present invention also relates to method and apparatus for mounting a printing plate, especially, a digitally made flexible printing plate, onto a plate cylinder of a printing apparatus.
In a lithographic printing apparatus, generally, a printing plate is wound around and fixed to a plate cylinder and, in this state, printing is executed.
However, a lithographic printing plate (in the present specification, this is referred to as a flexible printing plate), which uses as a support member a member formed of other material than metal inexpensive and easy to handle (for example, a plastic film or paper), has a weak point in dimensional stability. For example, the flexible printing plate can be deformed depending on the way of handling of the flexible printing plate when it is mounted or due to a frictional force between a rubber cylinder and itself during printing, which can degrade the printing dimension as well as the printing position accuracy with respect to paper.
Therefore, use of the flexible printing plate of the above type, conventionally, is limited to a simple printing which prints a relatively small number of printings and does not require the high matching accuracy of the printings; that is, such flexible printing plate has not been employed in a high-quality printing using multiple colors and requiring great delicacy or in a full-dress printing using a large-scale printing machine.
Here, description will be given in detail of the above-mentioned deformation that is caused depending on the way of handling of the flexible printing plate when it is mounted. In FIGS. 19 and 20, there is shown a typical printing plate-mounting apparatus. Specifically, FIG. 20 is a view of the printing plate-mounting apparatus when it is viewed from the direction of the arrow mark X shown in FIG. 19; and, FIG. 19 is a section view taken along the line Yxe2x80x94Y shown in FIG. 20.
As shown in FIG. 19, the plate cylinder 61 of the printing machine is structured such that a portion of a cylinder is cut away along the axial direction of the cylinder and, in a substantially flat surface (which is hereinafter referred to as a flat surface portion 61a, which is the cut face of the cutaway portion of the cylinder), there is formed a groove portion 65. And, within the groove portion 65, there are disposed a plate front end clamp mechanism 62 for holding the front end or leading end of a printing plate 70, and a plate rear end clamp mechanism 63 for holding the rear end or trailing end of the printing plate 70. The clamp mechanisms 62 and 63 respectively include lower teeth 62b and 63b (the upper surfaces of which are substantially flush with the flat surface portions 61a), and upper teeth 62a and 63a which are rotatably supported by their respective lower teeth and are capable of holding the plate front end or rear end between the upper surfaces of their respective lower teeth and themselves. Further, there is disposed a position adjusting mechanism (not shown) which is capable of adjusting the positions of the plate front end clamp mechanism 62 and plate rear end clamp mechanism 63 in the back-and-forth direction, in the right-and-left direction and in the oblique direction on the bottom surface of the groove portion 65.
Between the two flat surface portions 61a and curved surface portion 61b of the plate cylinder 61, there are formed top portions 61c respectively. Although not shown, there is known another type of plate cylinder in which there are formed top portions between the upper surfaces of the lower teeth of the clamp mechanisms, instead of the flat surface portions, and the curved portion of the plate cylinder.
Normally, the portions of the plate cylinder 61, where the two flat surface portions 61a and curved surface portion 61b cross each other, are each rounded to thereby provide a curved surface having a radius of 5-30 mm. It should be noted here that, in the present specification, such curved surface portions are also referred to as top portions.
And, as shown in FIG. 20, two positioning pins 64 are respectively provided on and projected from the upper surface of the lower tooth 62b of the plate front end clamp mechanism; specifically, at two positions of the lower tooth 62b upper surface which are spaced from each other in the axial direction of the plate cylinder 61. At the positions of the upper surface 62 of the plate front end clamp mechanism that correspond to the positioning pins 64, there are formed notches 66 respectively. Also, in the front end portion 70a of the printing plate 70 which is shown by a two-dot chained line in FIG. 20; specifically, at the positions of the front end portion 70a that correspond to the positioning pins 64, there are also formed two notches 71 respectively.
Recently, as printings have been turned into small lots and diversified, there has increased the need for a plate (which, in the present specification, is referred to as a flexible plate comprising a support member formed of material which is inexpensive and easy to handle (for example, plastic film, paper) other than metal, and a photosensitive layer disposed on such support member. However, since such plate is high in flexibility, there arise several problems when it is mounted on the plate cylinder.
For example, there is generally known a case where the flexible printing plate 70 is mounted onto the plate cylinder 61 using the printing plate-mounting apparatus shown in FIGS. 7 and 8. Specifically, in this case, when, while holding the plate rear end 70b, an operator pushes the plate front end 70a of the printing plate between the upper tooth 62a and lower tooth 62b of the plate front end clamp mechanism to thereby bring the plate front end 70a into contact with two positioning pins 64, there is a fear that the plate front end 70a can be deformed and can be fixed in such deformed state. That is, in a plate cylinder capable of mounting thereon a printing plate of a half-kiku size or more, the distance between the two positioning pins 64 in the plate cylinder 61 is fairly wide; and, therefore, when mounting the printing plate 70 onto the plate cylinder 61, in case where the operator overpushes the printing plate 70 even slightly, the printing plate 70 can be deformed in such a manner that the plate front end 70a is projected in the pushing direction from between the two positioning pins 64. However, in case where the operator pushes the printing plate 70 insufficiently in order to avoid such deformation of the printing plate 70, the printing plate 70 cannot be positioned accurately.
As described above, the mountability of the flexible plate onto the plate cylinder is poor and thus it is difficult to always mount the flexible plate onto the plate cylinder in a constant state. Therefore, there are necessary a plurality of plate cylinders and thus, in case where the flexible plate is used in a multicolor printing (for example, four-color printing) which requires strict matching between the plate cylinders, mismatching can occur.
Also, as shown in FIG. 19, in the vicinity of the top portions 61c respectively formed between the flat surface portions 61a and curved portion 61b of the plate cylinder 61, the flexible printing plate 70 does not easily stick to the outer peripheral surface of the plate cylinder 61 but the flexible printing plate 70 tends to float up from the outer peripheral surface of the plate cylinder 61.
In order to prevent such flotation of the printing plate 70, an operator, while pulling strongly the plate rear end of the printing plate 70 with the plate front end thereof held by the plate front end clamp mechanism 62, rotates the plate cylinder to thereby wind the printing plate 70 onto the plate cylinder. In this case, however, the strongly pulled portion of the plate rear end of the flexible printing plate 70 is stretched loosely.
After the printing plate is wound onto the plate cylinder while pulling the plate rear end in the above-mentioned manner, the plate rear end of the printing plate is pushed into between the upper and lower teeth of the plate rear end clamp mechanism, the upper tooth is rotated to thereby fix the plate rear end, and, using a tension apply mechanism (not shown), the plate rear end clamp mechanism is moved in a direction where a tensile force is applied to the printing plate, thereby bringing the printing plate into close contact with the peripheral surface of the plate cylinder, which completes the mounting of the printing plate onto the plate cylinder.
However, in an ordinary conventional plate-mounting apparatus, the tension apply mechanism for contacting the flexible printing plate with the peripheral surface of the plate cylinder closely is designed in combination with a printing plate having a support member formed of metal such as aluminum; and, therefore, in the case of the flexible printing plate, it is stretched more than necessary.
Also, in case where the tension apply mechanism is designed such that it can apply a lower tensile force according to the flexible printing plate, the tensile force applied is too weak to closely contact the printing plate with the plate cylinder. Even if the printing plate can be mounted onto the plate cylinder in such a manner that the printing plate is prevented from floating up from the plate cylinder, in the case of such weak tensile force, the printing plate deviates in position due to a frictional force which is produced between a rubber cylinder and itself in printing.
Recently, in a lithographic printing method, due to the enhancement in the latest digital picture drawing technology as well as due to the need for enhancement in the efficiency of processing, there have been proposed a large number of systems for drawing digital image information directly on a printing plate. This is a technology which is referred to as CTP (Computer-to-plate) or DDPP (Digital Direct Printing Plate).
This technology is advantageous over a conventional plate making method (which provides close-contact exposure with a lith film superimposed on top of a printing plate) in that it can provide better image position accuracy with respect to a flexible printing plate and better matching accuracy in a multicolor printing.
Of course, there is also proposed a digital reprographic (plate making) system using a flexible printing plate; and, because it is inexpensive, there exists the need for a multicolor printing using this system. However, since the flexible printing plate has the above-mentioned problems, it cannot make the best use of its advantage that it can provide excellent image position accuracy in the digital reprography; and, therefore, in a multicolor printing, it has not been able to realize matching accuracy equivalent to that of the printing plate having a metal support member.
The present invention aims at eliminating the above-mentioned drawbacks.
Accordingly, an object of the invention is to provide a flexible plate-mounting member which is capable of mounting a flexible plate onto a plate cylinder positively and easily.
Another object of the invention to provide flexible printing plate-mounting method and apparatus which is capable of mounting a digitally-made flexible printing plate easily without deforming the same, allows the flexible printing plate to be applied to a conventional printing machine with slight improvements, and allows the flexible printing plate to provide dimensional stability equivalent to that of a metal support member printing plate as well as matching accuracy in a multicolor printing.
Other objects and effects of the present invention will become apparent from the following description.
In a first aspect, the present invention relates to the following items (1-1) to (1-3).
(1-1) A plate-mounting member to be attached to a plate front end of a flexible plate in order to mount said flexible plate having a plurality of fixing holes onto a plate cylinder including a plate front end clamp mechanism having upper and lower teeth and at least two positioning pins disposed between upper and lower teeth, said plate-mounting member comprising a base and a plurality of fixing pins disposed on said base to be respectively inserted into said plurality of fixing holes formed in said plate front end, wherein said base is to be attached to said positioning pins disposed in said plate front end clamp mechanism to thereby position said plate front end.
(1-2) The plate-mounting member according to item (1-1) above, wherein said plurality of fixing pins are disposed on said base along the width direction of said plate and the distance between adjacent fixing pins is not more than 400 mm.
(1-3) The plate-mounting member according to item (1-1) or (1-2) above, wherein deformation preventive notches are formed in the portions of said base that are to be held by said upper and lower teeth.
In a second aspect, the present invention relates to the following items (2-1) to (2-13).
(2-1) A flexible printing plate-mounting method for mounting a flexible printing plate having three or more notches formed in a plate front end thereof onto a plate cylinder, comprising the steps of:
providing a flexible printing plate-mounting apparatus comprising:
a plate front end positioning and fixing mechanism comprising: a plate front end clamp mechanism having upper teeth and lower teeth for fixing the plate front end of said printing plate to said plate cylinder; and at least three positioning pins respectively disposed in said plate front end clamp mechanism in such a manner that they are respectively opposed to said notches of said printing plate;
a printing plate pressure mechanism for pressing said printing plate against said plate cylinder;
a plate rear end fixing mechanism for fixing the plate rear end of said printing plate to said plate cylinder; and
a packing sheet which is wound and fixed to said plate cylinder and has a function of preventing positional deviation of said printing plate;
positioning and fixing said plate front end to said plate cylinder by inserting the plate front end of said printing plate into between said upper and lower teeth of said plate front end clamp mechanism to contact the inner peripheral surfaces of said notches of said plate front end with said at least three positioning pins;
winding said printing plate onto said plate cylinder by rotating said plate cylinder with said plate rear end set free, while said printing plate pressure mechanism presses said printing plate against the entire outer peripheral surface of said plate cylinder including top portions thereof using a pressure member; and
pressing and fixing said plate rear end of said printing plate in a radial direction of said plate cylinder using said plate rear end fixing mechanism after completion of said winding;
whereby stretching of said flexible printing plate in its maximum printing length in the rotational direction of said plate cylinder during said printing plate-mounting operation is suppressed to 100 xcexcm or less.
(2-2) A flexible printing plate-mounting method for mounting a flexible printing plate having at least three fixing holes formed in a plate front end thereof onto a plate cylinder, comprising the steps of:
providing a flexible printing plate-mounting apparatus comprising:
a plate front end positioning and fixing mechanism comprising: a plate front end clamp mechanism having upper teeth and lower teeth for fixing the plate front end of said printing plate to said plate cylinder; positioning pins disposed in said plate front end clamp mechanism; and a pin contact member which has higher rigidity than said printing plate, is to be attached to said positioning pin and has at least three fixing pins for fixing said printing plate;
a printing plate pressure mechanism for pressing said printing plate against said plate cylinder;
a plate rear end fixing mechanism for fixing the plate rear end of said printing plate to said plate cylinder; and
a packing sheet which is wound and fixed to said plate cylinder and has a function of preventing positional deviation of said printing plate;
positioning and fixing said plate front end to said plate cylinder by allowing said fixing holes of said printing plate to be inserted with said fixing pins of said pin contact member between said upper and lower teeth of said plate front end clamp mechanism;
winding said printing plate onto said plate cylinder by rotating said plate cylinder with said plate rear end set free, while said printing plate pressure mechanism presses said printing plate against the entire outer peripheral surface of said plate cylinder including top portions thereof using a pressure member; and
pressing and fixing said plate rear end of said printing plate in a radial direction of said plate cylinder using said plate rear end fixing mechanism after completion of said winding;
whereby stretching of said flexible printing plate in its maximum printing length in the rotational direction of said plate cylinder during said printing plate-mounting operation is suppressed to 100 xcexcm or less.
(2-3) A flexible printing plate-mounting method for mounting a flexible printing plate having at least three fixing holes formed in a plate front end thereof onto a plate cylinder, comprising the steps of:
providing a flexible printing plate-mounting apparatus comprising:
a plate front end positioning and fixing mechanism comprising: a plate front end clamp mechanism having upper teeth and lower teeth for fixing the plate front end of said printing plate to said plate cylinder; and a positioning pin disposed in said plate front end clamp mechanism;
a printing plate pressure mechanism for pressing said printing plate against said plate cylinder;
a plate rear end fixing mechanism for fixing the plate rear end of said printing plate to said plate cylinder;
a packing sheet which is wound and fixed to said plate cylinder and has a function of preventing positional deviation of said printing plate; and
a pin contact member which has higher rigidity than said printing plate and includes at least three fixing pins for fixing said printing plate;
fixing said printing plate on said pin contact member by allowing said fixing holes of said printing plate to be inserted into said fixing pins of said pin contact members respectively;
fixing and positioning said printing plate onto said plate cylinder by fixing a leading end of said pin contact member to said positioning pin between said upper and lower teeth of said plate front end clamp mechanism;
winding said printing plate onto said plate cylinder by rotating said plate cylinder with said plate rear end set free, while said printing plate pressure mechanism presses said printing plate against the entire outer peripheral surface of said plate cylinder including top portions thereof using a pressure member; and
pressing and fixing said plate rear end of said printing plate in a radial direction of said plate cylinder using said plate rear end fixing mechanism after completion of said winding;
whereby stretching of said flexible printing plate in, its maximum printing length in the rotational direction of said plate cylinder during said printing plate-mounting operation is suppressed to 100 xcexcm or less.
(2-4) The flexible printing plate-mounting method according to any one of items (2-1) to (2-3) above, wherein said packing sheet has at least one roughened surface, and said packing sheet is wound and fixed onto said plate cylinder in such a manner that said roughened surface side becomes an outer surface side.
(2-5) The flexible printing plate-mounting method according to any one of items (2-1) to (2-3) above, wherein said packing sheet has at least one sticky surface, and said packing sheet is wound and fixed onto said plate cylinder in such a manner that said sticky surface side becomes an outer surface side.
(2-6) The flexible printing plate-mounting method according to any one of items (2-1) to (2-5) above, wherein said flexible printing plate-mounting apparatus further comprises a guide member for holding said printing plate, wherein said guide member holds said printing plate, before and during mounting said printing plate onto said plate cylinder, in such a manner that the plate rear end thereof is set free.
(2-7) A flexible printing plate-mounting apparatus for mounting a flexible printing plate having three or more notches formed in a plate front end thereof onto a plate cylinder, said flexible printing plate-mounting apparatus comprising:
a plate front end positioning and fixing mechanism comprising: a plate front end clamp mechanism having upper teeth and lower teeth for fixing the plate front end of said printing plate to said plate cylinder; and at least three positioning pins respectively disposed in said plate front end clamp mechanism in such a manner that they are respectively opposed to said notches of said printing plate;
a printing plate pressure mechanism for pressing said printing plate against said plate cylinder;
a plate rear end fixing mechanism for fixing the plate rear end of said printing plate to said plate cylinder; and
a packing sheet which is wound and fixed to said plate cylinder and has a function of preventing positional deviation of said printing plate.
(2-8) A flexible printing plate-mounting apparatus for mounting a flexible printing plate onto a plate cylinder, said flexible printing plate-mounting apparatus comprising:
a plate front end positioning and fixing mechanism comprising: a plate front end clamp mechanism having upper teeth and lower teeth for fixing the plate front end of said printing plate to said plate cylinder; positioning pins disposed in said plate front end clamp mechanism; and a pin contact member which has higher rigidity than said printing plate, is to be attached to said positioning pin and has at least three fixing pins for fixing said printing plate;
a printing plate pressure mechanism for pressing said printing plate against said plate cylinder;
a plate rear end fixing mechanism for fixing the plate rear end of said printing plate to said plate cylinder; and
a packing sheet which is wound and fixed to said plate cylinder and has a function of preventing positional deviation of said printing plate.
(2-9) A flexible printing plate-mounting apparatus for mounting a flexible printing plate onto a plate cylinder, said flexible printing plate-mounting apparatus comprising:
a plate front end positioning and fixing mechanism comprising: a plate front end clamp mechanism having upper teeth and lower teeth for fixing the plate front end of said printing plate to said plate cylinder; and a positioning pin disposed in said plate front end clamp mechanism;
a printing plate pressure mechanism for pressing said printing plate against said plate cylinder;
a plate rear end fixing mechanism for fixing the plate rear end of said printing plate to said plate cylinder;
a packing sheet which is wound and fixed to said plate cylinder and has a function of preventing positional deviation of said printing plate; and
a pin contact member which has higher rigidity than said printing plate and includes at least three fixing pins for fixing said printing plate.
(2-10) The flexible printing plate-mounting apparatus according to any one of items (2-7) to (2-9) above, wherein said packing sheet has at least one roughened surface, and said packing sheet is wound and fixed onto said plate cylinder in such a manner that said roughened surface side becomes an outer surface side.
(2-11) The flexible printing plate-mounting apparatus according to any one of items (2-7) to (2-9) above, wherein said packing sheet has at least one sticky surface, and said packing sheet is wound and fixed onto said plate cylinder in such a manner that said sticky surface side becomes an outer surface side.
(2-12) The flexible printing plate-mounting apparatus according to any one of items (2-7) to (2-11), further comprising a guide member for holding said printing plate, before and during mounting said printing plate onto said plate cylinder, in such a manner that the plate rear end thereof is set free.
(2-13) The flexible printing plate-mounting apparatus according to any one of items (2-7) to (2-12), further comprising:
a rotating member for rotating said plate cylinder when mounting said printing plate onto said plate cylinder;
a detector for detecting the rotational position of said plate cylinder;
a rotation controller for controlling the rotation and stopping of said plate cylinder rotating member at given positions in accordance with signals from said rotational position detector;
a driving member for driving said pressure member so as to be into contact with or separated from said plate cylinder; and
a controller for controlling said driving member at given positions in accordance with signals from said rotational position detector.